The present invention is especially designed to assemble stacks or "cubes" of concrete block in which each tier of the multi-tiered stack will consist of several blocks, as for example twelve blocks arranged in four rows and three columns. Because each tier or layer is made up of a plurality of individual articles, most prior art arrangements for forming such stacks have found it necessary at some stage to locate a support platform beneath the tier which must subsequently be withdrawn from beneath the tier to deposit the supported tier upon an underlying tier. Since the platform must be of finite thickness, this requires the articles to tilt and drop from the retracting edge of the support platform. Other arrangements employ cooperating interleaving tine systems in which the load is transferred from one tine system to the other in alternation, such arrangements requiring a rather complex mechanical system--see for example Thibault U.S. Pat. No. 3,904,045.